sweaty booty
just as the word indicates-sweat congregating on the rear end pants/skirt seat of a person. It comes from different ways, heat/humidity, obesity, sitting, working out, sex-but is usually only somewhat attractive when a person with a toned body dances so vigorously they get it over the course of an evening of partying.
Sue and Dan have strut their stuff so much tonight on the dance floor, that they both have earned a place in the sweaty booty hall of fame. Their riding home in your car later.